China develops water-skimming plane

Wednesday, July 11th, 2007

China develops a water-skimming plane:

Chinese scientists have developed a “Wing-In-Ground” (WIG) aircraft which can fly long distances just a few feet above the sea surface, state media said on Wednesday.

The plane can fly as low as half a meter (1 ft 7 ins) off the surface, hitting speeds of up to 300 km (180 miles) per hour and can carry up to 4 tonnes on takeoff.

“It’s as safe as ships, although five or six times faster,” associate professor Xu Zhengyu, vice-president of the research team at Tongji University in Shanghai, was quoted as saying.

“And it can carry much more weight than ordinary planes while costing half as much and using half as much fuel.”

Wing In Ground effect refers to the reduction in drag experienced by an aircraft as it approaches a height approximately twice a wingspan’s length off the ground or other level surface such as the sea.

China, of course, is not the first nation to develop a WIG craft:

Though ground effect has been known since the early days of flight, most pilots regarded it as nothing more than a nuisance that changed the flying qualities of their aircraft during takeoff and landing. Nevertheless, many researchers soon realized that this phenomenon could be exploited to produce a new class of highly efficient craft known as WIG vehicles. Most of the pioneering research into these vehicles was performed in West Germany and the Soviet Union.

Perhaps the most successful researcher in this field was Rostislav Alexeiev, head of the Central Hydrofoil Design Bureau in the Soviet Union from the 1950s through the early 1970s. Alexeiev began his career developing hydrofoils, which are boats fitted with underwater wings. When the boat moves, these wing create lift that pulls the boat hull up and out of the water and allows the craft to cruise at higher speeds. But Alexeiev quickly realized that a hydrofoil can only go so fast due to the drag created by the dense water through which it “flies.” Why not instead raise the entire vehicle out of the water and cruise at even higher speeds, he reasoned. This line of thought led to a new vehicle with wings above the surface of the water, a vehicle the size of a boat and able to carry a massive payload but able to cruise at the speed of an aircraft. Another advantage of such a vehicle would be the ability to fly at very low altitudes, below the detection range of enemy radar. Alexeiev dubbed this new class of vehicle the Ekranoplan, which is Russian for “screen plane.” His early designs were numbered under the SM series, an acronym standing for Samorodnaya Model, meaning “self sustained craft.”

Alexeiev developed a number of sub-scale designs in experimental tests that culminated in 1965 with the completion of the KM , the largest WIG vehicle ever built. Making its first flight on 18 October 1966, the KM was powered by a whopping 10 turbojet engines and weighed up to 540 tons. Eight of the engines were mounted near the vehicle’s nose so that their thrust could be deflected underneath the wing to create an initial cushion of air that raised the KM out of the water. Once the craft was traveling fast enough that the wings generated sufficient lift to keep the vehicle above the water, the thrust was redirected aft to increase velocity.

The KM was modified numerous times to evaluate the effects of different design elements. Among these changes included varying the wingspan from 105 ft (32 m) to 131 ft (40 m) and increasing the fuselage length from 302 ft (92 m) to 347 ft (106 m). The KM, also dubbed the Caspian Sea Monster by American observers who spotted the craft in satellite surveillance, remained in use until 1980 when it crashed during takeoff.

Although Alexeiev passed away in 1980, his design bureau continued to build and test Ekranoplans until the collapse of the Soviet Union. One of the more successful concepts was the Lun, which began trials on the Caspian Sea in 1987. The Lun was of similar design to the KM but smaller and built to carry anti-ship cruise missiles for high-speed attacks against American carrier battle groups.

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